Receiving against legacy inventory organization

We are implementing a new Oracle module and we have changed all our part numbers, changed from standard cost to average cost among other things, so we created a new inventory organization and a new item master. Initially it was planned that we would stop using the old organization and create new POs for anything that had not yet been received with the new item numbers. At the last minute, changes in the plan were made (we are still moving to the new organization on Monday), but we now want to continue using the old organization and receive against those